1. Field of the Invention
The present invention relates to a process for forming a pattern.
More particularly, the present invention relates to a process for forming a pattern in which a thin film on a substrate is etched by using a resist film formed by a multi-layer process as a mask, to thus form a pattern, followed by removing the mask.
2. Description of the Related Art
Due to the necessity for treating a large amount of information at a high speed on an integrated semiconductor device, which plays a main role in an information treating device, large-scale integrated circuits (LSI) and very large-scale integrated circuits (VLSI) have been developed and are now in practical use.
Recently, the demand for the precise forming of a fine pattern has greatly increased, accompanied by a fine-forming of a minimum design rule for LSI's and VLSI's.
To meet this demand, the multi-layer resist process has attracted attention as a replacement for a prior mono-layer resist process now widely employed.
A resist pattern formed by the multi-layer resist process has the following merits. For example, the usable focus range of the resist can be widened because the exposure is carried out after a leveling of the differences in the level of the substrate, by using the resist layer, and the patterning controllability is superior because the patterning is carried out by using an anisotropic etching process. Due to these merits, this multi-layer resist process is considered to have great possibilities in the field of manufacturing semiconductor devices, and this process is now proving to be an effective resist pattern process for obtaining half-micron patterns.
In the etching process, wherein the resist formed by the former multi-layer resist process is used as a mask, the formed multi-layer resist is used as is, followed by etching each kind of material to be etched.
For example, the resist layer having a silicon-containing layer thereon was used as a mask in the etching step.
In the etching of the material to be etched, however, by using the formed resist layer as is, for example, when a thick silicon oxide layer or a thin aluminium alloy layer is to be etched, a mask layer such as a silicon-containing layer formed on a relatively thinner resist layer than the above-mentioned silicon oxide layer, or the aluminium alloy thin layer, is simultaneously removed by etching during the etching of the silicon oxide. Therefore, the remaining resist layer is composed of only an organic component, and thus no problem arises in an ashing of the resist by means of an oxygen plasma or oxygen downstream.
Nevertheless, if the etching rate for the mask layer such as the silicon-containing layer is low, when polycrystalline silicon (poly Si), tungsten (W), tungsten silicide (W Si.sub.2) or the like is to be etched, or if the thin layer to be etched is not thick enough, a part of the mask layer such as a silicon-containing layer formed on the resist layer remains after the etching of the thin layer.
This part of the mask layer such as a silicon-containing layer is adhered to the substrate in the ashing process of the resist layer as dust, and this has an adverse influence on the manufacturing yield of LSI's. This is because, when forming a thin layer on a patterned substrate, the dust forms unwanted projections or holes in the thin layer and prevents the thin layer from tightly adhering to the substrate.